The present invention relates to a gas laser oscillator having an optical axis that is matched with the axial direction of the discharge tube, and more particularly to a gas laser oscillator capable of obtaining a laser beam of high quality.
FIG. 4 is a schematic block diagram of a conventional gas laser oscillator. In FIG. 4, reference numeral 1 is a discharge tube made of glass or other dielectric material, and the inside of the discharge tube 1 is filled with laser gas, or laser gas is circulated by a gas circulating apparatus not shown in the drawing. Reference numerals 2 and 3 are electrodes disposed at both ends of the discharge tube 1, reference numeral 4 is a high voltage power source connected to the electrode 2 and electrode 3, and reference numeral 5 is a discharge space inside the discharge tube 1 lying between the electrode 2 and electrode 3. Reference numeral 6 is a fully reflective mirror disposed toward one opening of the discharge space 5, and reference numeral 7 is a partially reflective mirror disposed toward the other opening of the discharge space 5, and the fully reflective mirror 6 and partially reflective mirror 7 form an optical resonator. Reference numeral 8 is a laser beam emitted from the partially reflective mirror 7.
In the conventional gas laser oscillator, the operation is described below. Discharge occurs in the discharge space 5 between the electrode 2 and electrode 3 connected to the high voltage power source 4. By this discharge, the laser gas in the discharge space 5 is excited by the discharge energy. The excited laser gas is set in a state of resonance by the optical resonator formed by the fully reflective mirror 6 and partially reflective mirror 7, and being optically amplified by this resonance, the laser beam 8 is issued from the partially reflective mirror 7. This laser beam 8 is used in various applications of laser processing.
FIG. 5(a) and FIG. 5(b) are diagrams for explaining the operation of the optical resonator in the gas laser oscillator, showing more specifically the structure of the gas laser oscillator. In FIG. 4, only one discharge tube is shown, but generally, as shown in FIG. 5(a) and FIG. 5(b), plural discharge tubes 1 are disposed in series along the optical axis. Although mere cylindrical forms are expressed in FIG. 5(a) and FIG. 5(b), same as the discharge tube 1 in FIG. 4, an electrode 2 and an electrode 3 are disposed at both ends of each discharge tube 1, and a high voltage power source 4 is connected between each pair of electrodes, that is, electrode 2 and electrode 3, and a discharge space is formed inside of each discharge tube 1.
In the gas laser oscillator shown in FIG. 5(a) and FIG. 5(b), when discharge occurs in the discharge space 5, a standing wave 10 is formed. The property of this standing wave 10 is determined by the size of the resonance space 9 and the curvature of the fully reflective mirror 6 and partially reflective mirror 7. This property of standing wave is known as TEM (transverse electromagnetic) mode order. Generally the lower the TEM mode order, the better is the laser beam converging, and it is known that higher processing performance is obtained. For example, the smaller the inside diameter of the discharge tube 1, the narrower is the resonance space, and therefore oscillation of high-order TEM mode is suppressed, the TEM mode order becomes lower and light converging is enhanced, so that a laser beam of high processing performance is obtained.
On the other hand, in the gas laser oscillator having thus explained construction, of the electric energy supplied from the high voltage power source 4, all energy excluding the portion converted into the laser beam 8 becomes heat. Therefore, to maintain the parallelism between the fully reflective mirror 6 and partially reflective mirror 7 by preventing deformation due to this generated heat, it is necessary to cool the fully reflective mirror 6 and partially reflective mirror 7 and the peripheral parts supporting them.
Concerning cooling of the fully reflective mirror 6 and partially reflective mirror 7 and their peripheral parts in the conventional gas laser oscillator, as disclosed in Japanese Laid-open Patent No. 56-90588, the construction being shown in FIG. 8. As shown in FIG. 8, the fully reflective mirror 6 and partially reflective mirror 7 for resonance are respectively held by a flange 31 and a flange 32. By coupling these flanges 31 and 32 through a support element 33, the parallelism of the fully reflective mirror 6 and partially reflective mirror 7 necessary for laser oscillation is maintained. A passage 35 is provided inside the support element 33, and it is intended to cool by passing oil or other cooling medium in this passage 35. In the conventional gas laser oscillator, the passage 35 of the cooling medium inside the support element 33 was straight from the inlet to the outlet of the cooling medium.
The high voltage power source 4 is, as shown in FIG. 15, composed of a switching power source 44, a step-up transformer 45, and a rectifying and smoothing circuit 46. Generally, the gas laser oscillator is composed of plural discharge tubes, and each discharge tube requires the step-up transformer 45 and rectifying and smoothing circuit 46. In one switching power source 44, the primary side of plural step-up transformers 45 can be connected, and therefore only one switching power source 44 is enough for plural discharge tubes.
The step-up transformer 45 is composed of a step-up transformer main body 49 and a transformer container 47 as shown in FIG. 16, and the transformer container 47 is filled with insulating oil 48, and the step-up transformer main body 49 composed of coil and core is immersed in the insulating oil 48. A top plate 50 is disposed in the upper part of the transformer container 47, and an oil feed port 51 provided in the top plate 50 is sealed with an oil cap 52 except when feeding oil, so that the entire step-up transformer 44 is in a sealed structure.
The conventional gas laser oscillator thus constructed had several problems.
First, to lower the TEM mode order, in the discharge tube 1 shown in FIG. 5(a), when the inside diameter of the discharge tube 1 is reduced as shown in FIG. 5(b), scattered beam 8a is likely to occur in the resonance space 9, and scattered beam 8a mixes into the laser output. FIG. 6 shows an output mode in a conventional gas laser oscillator. The axis of abscissas in FIG. 6 denotes the distance toward outside from the center of the output laser beam, and position 0 indicates the center. The axis of ordinates represents the energy density of the laser beam. FIG. 6 shows that scattered beam 8a is present in the peripheral region A of the laser beam 8. Laser cutting by using such a laser beam causes an increase in the thermal effects around the cut section due to the scattered beam 8a included in the peripheral region, and lowers the cutting quality. As explained above, when attempting to improve the light converging and enhance the processing performance by lowering the TEM mode order, the scattered beam mixes into the output laser beam to increase the thermal effect range, which leads to a first problem of deterioration of processing quality.
As mentioned herein, in the gas laser oscillator, of the electric energy supplied from the high voltage power source 4, all energy except for the portion converted into the laser beam becomes heat 36. Such heat 36 was dissipated, conducting to the parts composing the gas laser oscillator, such as flanges 31 and 32 existing around the resonance space 9 or the support element 33 for coupling them, through the laser gas filling the resonance space 9 as shown in FIG. 9.
The support element 33 is a member for maintaining the parallelism between the fully reflective mirror 6 and partially reflective mirror 7, and when uniformity of temperature distribution in the support element 33 is lost due to the conducting heat 36, the support element 33 is thermally deformed, and accurate parallelism between the fully reflective mirror 6 and partially reflective mirror 7 cannot be maintained. To avoid this inconvenience, the support element was cooled by passing a cooling medium in the support element 33. However, in the conventional gas laser oscillator, the passage 35 for the cooling medium was straight from the inlet to the outlet of the cooling medium inside the support element 33. Accordingly, heat convection occurs in the cooling medium inside the passage 35, and temperature distribution of the cooling medium itself is not uniform. Due to heat convection of the cooling medium itself, the temperature is higher in the upper part and the temperature is lower in the lower part of the support element 33, and thus the temperature distribution is uneven, and thermal distortion occurs. This thermal distortion leads to a second problem of making it difficult to maintain the accurate parallelism between the fully reflective mirror 6 and partially reflective mirror 7.
In the step-up transformer 45 of the conventional high voltage power source, the step-up transformer main body 49 was contained in the transformer container 47, and the transformer container 47 was in a sealed structure. Due to the heat generated in the step-up transformer main body 49, the temperature of the insulating oil 48, in which the transformer main body 49 is immersed, and the air 53 in the transformer container 47 are raised. When the transformer container 47 is closed by the top plate 50 and oil cap 52, the internal atmospheric pressure in the transformer container is raised, and a pressure difference occurs between the inside and outside of the transformer container 47. This pressure difference causes the insulating oil 48 to leak out of the transformer container 47.
To eliminate the pressure difference between the inside and outside of the transformer container 47, as shown in FIG. 17, a penetration hole was provided in the oil cap 52. As a result, occurrence of a pressure difference between the inside and outside of the transformer container 47 could be prevented, but the insulating oil 48 splashed up and leaked during transportation. FIG. 18 and FIG. 19 are modified examples of the penetration hole provided in the oil cap 22, but it was a third problem that leakage of the insulating oil 48 could not be prevented completely.
The invention is devised to solve the above-described problems, and it is a first object thereof to offer a gas laser oscillator capable of obtaining a laser beam of high quality by suppressing occurrence of scattered beam while lowering the output laser TEM mode order.
It is a second object of the invention to offer a gas laser oscillator capable of maintaining parallelism of fully reflective mirror and partially reflective mirror for composing an optical resonator, and obtaining a stable laser beam, by preventing thermal deformation of the support element and other members due to heat generated by laser oscillation.
It is a third object of the invention to offer a gas laser oscillator capable of preventing the occurrence of pressure difference between inside and outside of the transformer container, and also preventing the insulating oil in the transformer container from leaking out during transportation.
The gas laser oscillator, constructed in accordance with a first embodiment of the invention, comprises:
at least three discharge tubes disposed in series along the optical axis of laser beam for forming a discharge space inside,
a fully reflective mirror disposed toward one opening of the discharge space for composing a terminal mirror,
a partially reflective mirror disposed toward the other opening of the discharge space for composing an output mirror, and
a spacer disposed between the partially reflective mirror and the closest discharge tube, having an opening in the center of the optical axis of laser beam.
The discharge tubes are disposed in series along the optical axis, the sum of lengths of a pair of discharge tubes disposed at both ends in the optical axis direction supposed to be L1, the inside diameter of these discharge tubes supposed to be r1, the sum of lengths of the other discharge tubes in the optical axis direction supposed to be L2, the inside diameter of these discharge tubes supposed to be r2, and the inside diameter of the opening of the spacer supposed to be r3 satisfy the following three formula simultaneously.
The gas laser oscillator of another embodiment of the invention comprises:
discharge tubes disposed along the optical axis of laser beam for forming a discharge space inside,
a fully reflective mirror disposed toward one opening of the discharge space for composing a terminal mirror,
a partially reflective mirror disposed toward other opening of the discharge space for composing an output mirror,
a first flange for holding the fully reflective mirror,
a second flange for holding the partially reflective mirror, and
a support element, being a member for keeping parallelism between the fully reflective mirror and the partially reflective mirror by coupling the first flange and the second flange, and having a spiral medium passage for passing cooling medium disposed inside thereof.
In the support element of the gas laser oscillator, plural spiral cooling medium passages are provided for passing cooling medium.
The gas laser oscillator also comprises:
discharge tubes disposed along the optical axis of laser beam for forming a discharge space inside,
a fully reflective mirror disposed toward one opening of the discharge space for composing a terminal mirror,
a partially reflective mirror disposed toward other opening of the discharge space for composing an output mirror, and
a high voltage power source including a switching power source for generating discharge inside the discharge tubes, a step-up transformer, and a rectifying and smoothing circuit,
in which the step-up transformer includes:
a step-up transformer main body,
a transformer container for storing insulating oil inside for immersing the step-up transformer main body in the inside insulating oil, and
an oil cap having a penetration hole and also including a filter having resistance to passing of insulating oil in the penetration hole, being fitted to the transformer container.
In the gas laser oscillator of the invention, the penetration hole provided in the oil cap of the transformer container penetrates the oil cap in the vertical direction, and is provided with a filter having resistance to passing of insulating oil at a lower portion in the penetration hole.
In the gas laser oscillator of the invention, the penetration hole provided in the oil cap of the transformer container has one end opened to the lower end of the oil cap, and other end opened to the outer circumference of the upper part of the oil cap, and is provided with a filter having resistance to passing of insulating oil at a lower portion in the penetration hole.
In the gas laser oscillator of the invention, the penetration hole provided in the oil cap of the transformer container has one end opened to the upper end of the oil cap, and other end opened to the outer circumference of the lower part of the oil cap, and is provided with a filter having resistance to passing of insulating oil at a lower portion in the penetration hole.
In the gas laser oscillator of the invention, the pore size of the filter of the oil cap disposed in the transformer container is 0.55 mm or less.
According to the first embodiment of the gas laser oscillator, of the series of discharge tubes arranged in series, the resonance space formed in the other discharge tubes other than a pair of discharge tubes disposed at both ends is relatively narrowed, the TEM mode order of the laser beam is lowered. Besides, since scattered beam caused in the discharge tubes disposed at ends is intercepted by the spacer and is not delivered outside, so that mixing of scattered beam into the laser beam is prevented. The TEM mode order of the laser beam is lowered, light converging is improved, and mixing of scattered beams into the laser beam is prevented, so that an excellent laser beam high in processing performance and small in thermal effects in the processing peripheral area is obtained.
According to the gas laser oscillator of the second embodiment, by forming the passage for cooling medium inside the supporting element spirally, the temperature distribution of the support element is uniform, and thermal distortion of the support element can be eliminated. Since the support element is formed by coupling the flange for holding the fully reflective mirror and the flange for holding the partially reflective mirror, as the thermal distortion of the support element is eliminated, it is easier to maintain the parallelism between the fully reflective mirror and partially reflective mirror, so that a stable laser beam can be obtained.
According to the gas laser oscillator of the second embodiment, by forming a penetration hole in the oil cap of the transformer container, and disposing a filter for resisting passing of insulating oil in this penetration hole, if the insulating oil splashes due to vibration during transportation, the insulating oil will never leak out of the transformer container. Besides, since the oil film formed in the filter provided in the penetration hole is easily broken by the pressure difference between inside and outside of the transformer container, the internal pressure of the transformer container is nearly kept constant, and insulating oil will not leak out due to the pressure difference between inside and outside.